This invention relates to a marine power steering system and more particularly to an improved, compact, high efficiency hydraulically assisted system.
There have been proposed power assisted marine steering systems. These types of systems generally employ hydraulic assist motors that are mechanically coupled to the watercraft steering device to apply a force that assists the manual inputted steering force. These prior art systems have several disadvantages as will become apparent by reference to FIG. 1, that shows a conventional type of system now used.
Referring now to FIG. 1, a manually operated steering control, such as a steering wheel 11 is mounted in the operator""s area of the associated watercraft and its output is connected to a vessel steering device 12 by a Bowden wire actuator, indicated generally at 13. The watercraft steering device 12 may comprise any known type of watercraft steering device such as a rudder or pivotally supported propulsion device such as an outboard motor or the outboard drive portion of an inboard outboard drive.
The Bowden wire actuator is comprised of an inner, actuating wire 14 and a surrounding protective sheath 15. One end of the inner wire is connected to the steering wheel 11 and the other end is connected to the watercraft steering device 12. These connections are of any known type.
A hydraulic assist motor 59 is also connected to the vessel steering device 12 to assist in the steering operation. The assist motor is generally a reciprocating motor comprised of an outer cylinder 17 having a cylinder bore 18 in which a piston 19 is reciprocally mounted to define a pair of fluid chambers 21 and 22. During steering assist one or the other of the chambers 21 and 22 is pressurized and the fluid from the other is returned to an oil reservoir 23. How this is done will be described shortly.
A piston rod 24 is connected to the piston 19 at one end and extends through the chamber 22, externally of the cylinder 17 for connection to the vessel steering device 12.
The power assist is controlled by controlling the pressurization of either the chamber 21 or 22 from a fluid pump 25 that is continuously driven by an engine 26 which generally is the engine that powers the associated watercraft. The supply and return of the fluid to the motor 26 is controlled by a spool valve, indicated generally at 27. The spool 28 of the valve 27 is connected to the sheath 15 of the Bowden wire actuator 13. As is well known, the force applied to the wire 14 from the steering wheel 11 causes a reactive force on the sheath 15 and this force is utilized to actuate the valve spool 28.
This type of system has a number of disadvantages. For example, the hydraulic pump 25 is constantly driven by the engine 26 while the engine 26 is powering the watercraft, resulting in loss of the engine output. In addition, the hydraulic cylinder 16 and the hydraulic pump 25 are separately installed in the watercraft requiring, complicated hydraulic piping arrangement for connection. This also results in more burdensome installation as well as a risk of foreign matter entering into the hydraulic circuit.
It has been proposed to utilize an electric motor to drive the pump 25, but this does not simplify the plumbing problems. In addition the motor is operated continuously to insure the availability of hydraulic assist, putting added load on the watercraft electrical system and its batteries. Also it means that the system must be constantly pressurized and this reduces the life of the system.
It is, therefore, a principal object of this invention to provide an improved and simplified water craft steering assist system that has a reduced and simplified hydraulic system and a simplified control and operator therefore.
This invention is adapted to be embodied in an assisted marine steering system that is comprised of a manually operated steering control, a watercraft steering device controlling the direction of travel of a watercraft and a manual connection between the manually operated steering control and the watercraft steering device for manually operating the watercraft steering device. A force sensor is provided for sensing the manual force applied to the manually operated steering control. A hydraulic assist motor is coupled to the watercraft steering device for applying a hydraulic assist to the steering operation thereof. Finally, a control varies the amount of hydraulic assist outputted to the watercraft steering device by the hydraulic assist motor in response to the amount of manual force sensed by the force sensor.